1. Field of the Invention
The present invention is directed to an actuation device for a friction clutch which is arranged in the drivetrain of a motor vehicle between a drive unit and a transmission, comprising a pressure medium force cylinder arrangement by means of which the friction clutch can be actuated via a release member. A measuring arrangement detects an actual release and has a measuring member which is movement-coupled or can be movement-coupled with a mating member whose position represents the actual release. In particular, the invention is directed to an actuation device for a friction clutch arranged in the drivetrain of a motor vehicle between a drive unit and a transmission, comprising a release member for actuating the friction clutch, which release member is associated with a pressure medium force cylinder arrangement and is displaceable along a release path. A control/regulating valve arrangement is associated with the pressure medium force cylinder arrangement and pressure medium source and actuates the pressure medium force cylinder arrangement by a command variable and an actual quantity representing a position of the release member or depending on this position, a measuring arrangement which is associated with the control/regulating valve arrangement and serves to detect the actual quantity or a measured quantity dependent upon the actual quantity. The measuring arrangement has at least one measuring member which is arranged so as to be movable along a measurement path and which is in a movement coupling connection or can be brought into a movement coupling connection with a mating member formed by the release member or by a member of the actuation device or friction clutch which varies in position and whose position represents the actual quantity or measurement quantity.
2. Description of the Related Art
DE 198 22 285, to which U.S. Pat. No. 6,167,995 corresponds, and DE 197 16 641 disclose special actuation devices of the type mentioned in the introduction in which a measurement piston element of a hydraulic measurement cylinder (DE 198 22 285 A1) serving as measuring arrangement or a valve element of the control/regulating valve arrangement (DE 197 16 641 A1) serving at the same time as a measuring arrangement has a lateral groove in which a flange portion of a pneumatic ring piston engages, so that the measurement piston element and the pneumatic ring piston are driven along by tractive force and pressure force so as to produce the movement coupling connection. Such a construction of the movement coupling connection is disadvantageous in that in the case of a removable structural unit containing the measuring arrangement and possibly the control/regulating valve arrangement, the respective measuring member and the pneumatic piston element, after removal of the structural unit, must be moved into and held in axial positions matching one another exactly when the structural unit or an exchangeable structural unit is reinstalled so that the flange portion of the pneumatic ring piston can engage in the groove of the measuring member and so that the movement coupling connection can be produced. This is made even more difficult when no wear compensation is provided and the axial position of the pneumatic ring piston element corresponding to an engaged clutch wanders and different axial positions of the measuring member for the assembly and production of the movement coupling connection must be adjusted for different wear states of the friction clutch.
DE 198 22 285 and DE 197 16 641 disclose special actuation devices of the type mentioned in the introduction in which a measurement piston element of a hydraulic measurement cylinder (DE 198 22 285 A1) serving as measuring arrangement or a valve element of the control/regulating valve arrangement (DE 197 16 641 A1) serving at the same time as a measuring arrangement has a lateral groove in which a flange portion of a pneumatic ring piston engages, so that the measurement piston element and the pneumatic ring piston are driven along by tractive force and pressure force so as to produce the movement coupling connection. Such a construction of the movement coupling connection is disadvantageous in that in the case of a removable structural unit containing the measuring arrangement and possibly the control/regulating valve arrangement, the respective measuring member and the pneumatic piston element, after removal of the structural unit, must be moved into and held in axial positions matching one another exactly when the structural unit or an exchangeable structural unit is reinstalled so that the flange portion of the pneumatic ring piston can engage in the groove of the measuring member and so that the movement coupling connection can be produced. This is made even more difficult when no wear compensation is provided and the axial position of the pneumatic ring piston element corresponding to an engaged clutch wanders and different axial positions of the measuring member for the assembly and production of the movement coupling connection must be adjusted for different wear states of the friction clutch.
In order to facilitate assembly of the structural unit, it would be conceivable to move the pneumatic piston (generally at least one piston of the pressure medium force cylinder arrangement) and the measuring member for the assembly into a defined respective position, for example, the moved in end position, for instance, by means of a special lever mechanism provided for this purpose, e.g., through the clutch housing opening. However, a lever mechanism of this kind does not seem advantageous with respect to the elaborate construction necessitated by it.
The known solution with a groove in the measuring member, possibly the measurement piston element, which groove receives the flange portion of the actuation piston (release piston), is also disadvantageous insofar as the axial dimensioning of the groove and that of the flange portion can only be adapted to one another in a relatively expensive manner with respect to manufacturing technique to produce the engagement between the groove and flange portion without difficulty on the one hand and a tractive force driving engagement and pressure force driving engagement essentially without play between the piston and measurement piston element. Therefore, in general, separate steps are required in order to provide a displacing engagement between the measuring member and release piston essentially without play. For example, additional spring elements could be inserted into the groove which pretension the annular flange of the release piston and the measuring member in the direction of mutual contact at a surface of the measuring member limiting the groove axially and accordingly eliminate the axial movement play between the release piston and measuring member. However, the additional spring elements mean increased production costs and, beyond this, make it more difficult to introduce the annular flange of the release piston into the groove during assembly of the structural unit.
In contrast, one object of the present invention is to simplify the production of the movement coupled connection between the measuring member and the mating member. According to a first aspect of the invention, the measuring member is brought into a tractive force driving engagement with the mating member so as to be essentially free from play in that the measuring member and the mating member approach one another along the measurement path.
According to the invention, it is not required that the measuring member and the mating member are brought into and held in a defined axial position relative to one another in order to produce the movement coupled connection. Rather, the movement coupled connection can be produced by the movement of the measuring member and/or mating member along the measurement path, for example, after the assembly of a structural unit having the measuring arrangement, In the case of a hydraulic measurement cylinder, for example, in that a measurement piston element serving as measuring member moves out in the direction of the mating member which, for example, is formed by a portion of a pressure medium force piston, for example, of a pneumatic ring piston. Accordingly, it is possible to decouple the assembly of the structural unit from the production of the movement coupling connection, so that the assembly of the structural unit is substantially simplified.
The inventive idea is not only applicable for actuation devices in which the measurement path and the release path both extend in an essentially straight line and are essentially parallel to one another or to an axis of the friction clutch. Other geometries are also possible. The construction of the release member is also not at issue. As a rule, this release member is a release bearing arrangement for actuating the friction clutch and, with reference to an axis of the friction clutch, is movable essentially coaxial to the friction clutch, as is also the case in the prior art solutions mentioned above. The drive unit is generally an internal combustion engine. Depending on the construction of the transmission, the friction clutch can be a single clutch or multiple clutch (especially a double clutch in case of a transmission with two input shafts).
In a preferred embodiment, the measuring arrangement comprises at least one hydraulic measurement cylinder which detects the actual quantity or the measurement quantity and to which the measuring member is assigned. As in the prior art discussed above, the measuring member can comprise a measurement piston element of the measurement cylinder. A hydraulic measurement cylinder arrangement serving as measuring arrangement is taken into consideration particularly in connection with a control valve arrangement working on the principle of a pressure scale.
Alternatively, it is possible that the measuring arrangement is based on other working principles. For example, the measuring arrangement can comprise a sensor, for example, a potentiometer sensor or a magnet sensor, which emits an electric signal and detects the actual quantity or the measurement quantity and to which the measuring member is assigned. For example, the measuring member can comprise an input element of the sensor, for example, in the case of a linear potentiometer, a sliding element of the potentiometer.
In general, the pressure medium force cylinder arrangement is arranged inside a housing cover containing the friction clutch and may include a pressure medium force ring cylinder, preferably a pneumatic force ring cylinder, which surrounds a transmission input shaft. In this case, it is preferable that a measuring unit having the measuring member, possibly the measurement piston element, is constructed as a structural unit which is separate from the pressure medium force cylinder arrangement and which is arranged, at least in part, inside the housing cover, but is preferably accessible from the outside when the housing cover is connected with the drive unit and transmission and, most preferably, can be removed and installed. The structural unit can be mounted at the pressure medium force cylinder arrangement.
When, for purposes of installation and removal, the structural unit is to be moved along a mounting path leading through a housing cover opening and laterally directed with reference to the measurement path, assembly of the structural unit is nevertheless not difficult, since the movement coupling connection can be produced independent from the mounting of the structural unit. In order to facilitate removal of the structural unit, the tractive force driving engagement (and, where appropriate, a pressure force driving engagement) and, therefore, the movement coupled connection can be released (canceled), preferably by means of a lateral movement of the structural unit along the mounting path occurring while the structural unit is removed.
With respect to the structural unit, it is particularly preferred that this structural unit is an integral measurement and control/regulating valve unit which also comprises the control/regulating valve arrangement.
With regard to the movement coupling connection, it is suggested according to a first solution that the tractive force driving engagement is carried out by means of a catch coupling connection or snap-in coupling connection acting between the measuring member and the mating member.
The catch coupling connection or snap-in coupling connection preferably has a catch spring element or snap-in spring element which is fixed, preferably in a detachable manner, at one of either the measuring member or the mating member. The element is locked with an associated mating engagement element of the other one of either the measuring member or the mating member, or is in a snap-in connection or can be locked with the mating engagement element in the course of mutual approach along the measurement path or can be brought into a snap-in connection. In the locked or snapped in state of the mating engagement element, the element is elastically pretensioned in the direction of mutual contact of the measuring member and mating member for providing the essentially play-free tractive force driving engagement. The spring element is preferably fixed to or in the measuring member. For this purpose, it is suggested by way of further development that the spring element is inserted into a cutout of the measuring member which opens in the direction of the mating member and is preferably fixed therein by catching or snapping in and has an engagement portion which projects out of the cutout in direction of the mating member and which engages behind the counter-engagement element. Another possibility consists in that the spring element is fixed to an end portion of the measuring member which is closer to the mating member, preferably by locking or fixedly snapping in, and has an engagement portion which projects over the end portion in direction of the mating member and engages behind the mating engagement element.
In order to fix the spring element to the measuring member or in the measuring member, it has proved advantageous when the spring element has a snap-ring-like fastening portion which engages with the measuring member. The spring element can then be constructed in a particularly simple manner. In the event that the snap-ring-like fastening portion is arranged in the cutout and acts at the inner surface of the latter, the spring element can be mounted in the measuring member a particularly simple manner with a tubular mounting tool. If required, the spring element could also be removed again with a disassembling tool, e.g., a pincer-like tool.
According to another possible construction, the spring element has a body portion which is arranged in the cutout, generally extends along an axis of the measuring member and is constructed in a flat manner, which body portion acts at an inner surface of the cutout by two side edges defining the body portion with respect to a first lateral direction and preferably has at least one leaf spring portion which projects from the body portion in a second lateral direction, elastically supports the body portion at the inner surface and/or is fixed in the cutout, preferably snaps in behind a holding collar of the measuring member. A spring element of this kind can be produced in a particularly economical manner, for example, by stamping and forming a sheet material, preferably leaf spring material, having spring characteristics. Close tolerances can then be maintained economically in the width of the spring element with respect to the cutout, or bore hole as the case may be, of the measuring member in order to ensure a defined reference position, possibly a middle position, of the spring element in the measuring member. In order that the spring element can sit in the measuring member without play with respect to the relative axial position, the body portion can have, in an end area which is farther from the engagement portion and arranged in the cutout, at least one spring portion which acts elastically at the measuring member and which must be overcome when the spring element is mounted in the cutout and then elastically pretensions the body portion in the direction of an elastic engagement of the leaf spring portion with the holding collar.
According to another possible construction, the spring element has a spring tube portion which is arranged in the cutout, acts elastically at an inner surface of the cutout accompanied by radial pretensioning and is preferably snapped in behind a holding collar of the measuring member. The radial pretensioning serves to ensure freedom from play between the spring element and the measuring member. With respect to freedom from play, it is suggested in a further development that the spring pipe portion engages via an inclined surface with the inner surface of the cutout in such a way that the spring pipe portion is elastically pretensioned in the direction in which the spring pipe portion contacts the holding collar. For example, the measuring member can have an inclined surface arrangement in a rear region of the cutout acted upon by the spring pipe portion.
According to another approach, it is suggested that the tractive force driving engagement is carried out by means of a magnetic force coupling connection acting between the measuring member and the mating member. For example, the magnetic force coupling connection can comprise at least one magnet element fixed to either the measuring member or mating member, which magnet element cooperates with an associated magnetically attractable portion or mating magnet element of the other member in order to provide the tractive force driving engagement which is essentially free from play.
Producing the movement coupling connection by means of the magnetic force coupling connection is particularly advantageous in that a rotation of the release piston can occur successively in operation. When a portion of the release piston, possibly an annular flange of the piston as in the prior art, serves as a mating member, this can lead to problems when the movement coupling connection does not permit this rotating movement or permits it only accompanied by transmission of tilting forces to the measuring member. Such tilting forces or tilting moments, for example, on a measurement piston element serving as measuring member, could lead to measurement errors andxe2x80x94in case of the measurement piston elementxe2x80x94for example, to a self-locking of the hydraulic measurement cylinder. In spite of the high attraction forces in the direction along the measurement path, the magnetic force coupling connection allows relative transverse movements between the mating member and the measuring member due, for example, to a rotation of the release piston, without excessive transverse forces being transmitted to the measuring member. In order to minimize transverse forces of this kind, the magnet element and/or the magnetically attractable portion or magnet element can be constructed with a sliding surface at which the magnet element and the magnetically attractable portion or the mating magnet element engage with one another. Generally, it is suggested that means are associated with the measuring member and/or mating member for reducing counterforces acting against a transverse or rotational relative movement between the measuring member and mating member.
Particularly in the case of the catch coupling connection or snap-in coupling connection (but also possibly in differently constructed movement coupling connections such as the magnetic force coupling connection), it may be necessary to maintain a definite reference orientation, possibly a defined reference rotational position, of the measuring member relative to the mating member at least during the mounting process and while the movement coupling connection is being made. To ensure this, corresponding means can be provided. If required, the means can provide a defined angular position of the measurement piston element in a cylinder space of the measurement cylinder insofar as one exists. Further, the means can provide a defined angular position of the spring element, if any, relative to the measuring member, possibly the measurement piston element.
According to a second aspect of the invention, it is suggested for the actuation devices mentioned in the beginning that the measuring member is movement-coupled or can be movement-coupled with the mating member by means of a catch coupling connection or snap-in coupling connection acting between the measuring member and mating member and/or by mean of a magnetic force coupling connection acting between the measuring member and the mating member. In the movement-coupled state, the measuring member and the mating member can be in a tractive force driving engagement and/or rotational force driving engagement with one another essentially without play. The actuation device according to the invention can have further features of the actuation devices according to the first aspect of the invention as indicated above.
The invention is further directed to a drivetrain for a motor vehicle comprising a drive unit (possibly an internal combustion engine), a transmission and a friction clutch arranged between the drive unit and the transmission, and comprising an actuation device according to the invention.